1. Field of the Invention
The present invention relates to a poppet valve device for performing opening and closing of a high-pressure liquid passage, specifically to a poppet valve device to control the injection timing of an electronic controlled fuel injection apparatus for an internal combustion engine.
2. Description of the Related Art
In diesel engines, electronic controlled fuel injection apparatus have been widely used recently as an effective means for reducing atmospheric pollutants such as NOx (nitrogen oxides) and HC (hydrocarbons) (for example, see Japanese Laid-Open Patent Application Nos 2001-248479 and 2002-98024).
A poppet valve device driven by an electromagnetic valve device is used in each of these apparatuses for opening and closing the fuel passage in the apparatus.
FIG. 6 represents an example of a unit injector type electronic controlled fuel injection apparatus for a diesel engine. The unit injector like this is well known in the art and here brief explanation will be given. In the drawing, reference numeral 100 comprises a fuel injection pump part 101 and a fuel injection nozzle part 102. The fuel injection pump part 101 includes a poppet valve 5 and an electromagnetic valve device 20 for opening and closing the valve. A plunger 1 fitted into a pump case 3 is driven to reciprocate by way of a tappet 6, contact piece 7, plunger spring 8, etc. by means of a rocker arm 54 which is driven mechanically by the engine crank shaft to oscillate. A plunger chamber 25 is communicated to the injection nozzle part 102 via a fuel passage 052 on one side and communicated to the poppet valve 5 via a fuel passage 52 on the other side. The fuel passage 52 is communicated or discommunicated to a fuel passage 12 connecting to a fuel tank (not shown in the drawing) by opening or closing of the poppet valve 5, which is opened or closed by the electromagnetic valve device 20. The fuel injection nozzle part 102 includes a fuel injection nozzle 2 and a needle valve spring 51. The fuel pushed by a plunger 1 to be compressed in the plunger chamber 25 flows through the fuel passage 052 to a fuel pool 02 and is injected from the injection holes 02a. 
When the poppet valve 5 is opened, the pressure in the plunger chamber 25 does not increase by a down stroke of the plunger 1 because the plunger chamber 25 is communicated to the fuel tank through the fuel passage 52, through the poppet valve, and through the fuel passage 12. When the poppet valve 5 is closed, the pressure in the plunger chamber 25 increases as the plunger 1 moves down, and when the pressure in the fuel pool 02 reaches the needle-opening pressure, the needle valve 4 lifts up, overcoming the spring force of the needle valve spring 51, and the fuel begins to be injected from the injection holes 02a. During the fuel injection period, the amount of fuel compressed by the plunger is larger than that injected from the injection holes 02a of the injection nozzle 2 and the injection pressure increases with time. When the poppet valve is opened to communicate the plunger chamber 25 to the fuel tank, the pressure in the plunger chamber decreases rapidly, the pressure in the fuel pool 02 decreases rapidly, the needle valve is pushed down by the spring force of the needle valve spring 51 for the needle valve to be closed, and the injection is finished. In the succeeding lifting stroke of the plunger, fuel is sucked into the plunger chamber 25 through the fuel passage 12, poppet valve 5, and fuel passage 52.
An example of the conventional poppet valve used in an electronic controlled fuel injection apparatus for the purpose as above described is shown in FIG. 7(A) and FIG. 7(B) together with an electromagnetic valve. FIG. 7(A) shows the state in which the popped valve is opened, and FIG. 7(B) shows the state in which the poppet valve is closed. In the drawings, reference numeral 20 is an electromagnetic valve device, 3 is the pump case of a unit injector as explained above, and 52 is the fuel passage communicating to the plunger chamber of the unit injector. In the electromagnetic valve device 20, reference numerals 31 and 16 are valve cases, 031 is a solenoid housing inside the valve case 31, and 28 is a solenoid accommodated in the solenoid housing 031.
In an armature space 30, an armature 27 is fixed to the top of the poppet valve 5 by means of a bolt 29.
Reference numeral 10 is a valve seat member fixed in the pump case 3 by means of a fixing screw member 015. Reference numeral 033 is a passage hole drilled in the valve seat member 10 in the radial direction which allows an annular recess 05 of the poppet valve to communicate to an annular recess 17 of valve seat member 10. The recesses 05 and 17 are explained later. Reference numeral 5 is the poppet valve, which is fit in a through-hole of the valve seat member 10 for sliding and to the top of which is fixed the armature 27 by means of the bolt 29. Reference numeral 14 is a poppet valve spring disposed between the shoulder part of the poppet valve 5 and the ceiling part of the fixing screw member 015. The poppet valve 5 is pushed downward in the direction for the poppet valve 5 to be opened, that is, in the reverse direction of the attraction force of the armature 27. Reference numeral 05 is the annular recess formed along the periphery of the poppet valve 5, and reference numeral 17 is the annular recess formed along the periphery of the valve seat member 10. Reference numeral 12 is the supply and drain passage, one side thereof communicating to the annular recess 17 and the other side being connected to a fuel tank (not shown in the drawings). Reference numeral 10a is a seat face in the valve seat member 10 and 5a is a seat face of the poppet valve 5. The seat face 5a of the poppet valve sits on the seat face 10a of the valve seat member when closing the poppet valve. Accordingly, as the seat face 5a sits on or departs from the seat face 10a of the valve seat member 10, supply and drain passage 12 is discommunicated or communicated to the fuel passage 52 in the pump case 3. Reference numeral 07 is an axial passage communicating to an annular recess 06 formed along the inside circumference of the valve seat member 10, the axial passage 07 communicating to the fuel passage 52 which communicates to the plunger chamber of an injection pump not shown in FIG. 7(A) and FIG. 7(B). When the poppet valve 5 is closed, the fuel pressure is high in the recess 06 and low in the recess 05.
When electric current is shut off from flowing to the solenoid 28 of the electromagnetic valve device 20, the poppet valve 5 is pushed down by the spring force of the poppet valve spring 14, a gap “S” is developed between the upper surface of the armature 27 and the lower surface of the solenoid 28, the lower end face 5b of the poppet valve 5 contacts the bottom face 3a of the poppet valve device accommodating part of the pump case, the seat face 5a of the poppet valve 5 departs from the seat face 10a of the valve seat member 10, and the poppet valve is opened. Therefore, the plunger chamber 25 (see FIG. 6) is communicated to the supply and drain passage 12 through the fuel passage 52, the gap between the seat faces 5a and 10a developed by the departing of the seat face 5a from the seat face 10a, the passage hole 033 of the valve seat member 10, and the annular recess 17, and the fuel pushed down in the plunger chamber 25 as the plunger 1 (see FIG. 6) moves down is returned to the fuel tank via the fuel supply and drain pipe 12. Accordingly, fuel is not injected by the down stroke of the plunger 1.
When electric current flows to the solenoid 28 of the electromagnetic valve device 20, the armature 27 and the poppet valve 5 connected thereto are lifted up by the attraction generated in the solenoid 28 against the spring force of the valve seat spring 14 until the seat face 5a of the poppet valve 5 sits on the seat face 10a of the valve seat member 10, and the poppet valve is closed. Then the pressure rises in the plunger chamber 25 as the plunger 1 moves down, and the fuel pushed out from the plunger chamber 25 is injected from the injection holes 02a of the injection nozzle 2.
In recent years, the injection pressure is increasingly apt to be increased in order to enhance the effect of an electronic fuel injection apparatus to reduce atmospheric contaminants such as NOx and HC. The poppet valve device working in the electronic fuel injection apparatus as described above will be brought under more severe working conditions as fuel injection pressure increases.
However, with the poppet valve device of the prior art, there are problems in that cavitation erosion occurs in the poppet valve body and valve seat member due to the outburst of high-pressure fuel through the gap of the valve seat part, friction of sliding of the poppet valve body increases due to increased side thrust exerted on the poppet valve body, a crack occurs in the passage exposed to high-pressure liquid in the valve device and that bouncing occurs when the poppet valve opens, that is, when the seat face of the poppet valve body departs from the seat face of the valve seat member and the lower end face of the poppet valve contacts the bottom face of the poppet valve device accommodating part of the injection pump case.